NFC's Guidance for Mitigating & Remediating Mold on Lumber
Mold can be found almost anywhere and can grow on virtually any substance under warm, moist conditions. This can cause headaches for framing contractors because while mold differs from decay in that mold does not cause a decrease in the strength properties of lumber, it causes discoloration and/or odors on the lumber that customers object to.
“I’m involved in both the framing and component business and I’ve talked to a lot of people who do mold remediation for a living,” says Kenny Shifflett, owner of Ace Carpentry. “In all my research, it’s become clear this is an important issue for our industry to know the facts about.”
Mold cannot be eliminated, but it’s spread can be mitigated, and existing mold growth can be removed, through some straight-forward jobsite best practices. With regard to wood fiber, the most effective approach is to ensure its moisture content does not remain high for extended periods of time. Standing water should be removed from horizontal wood surfaces and wood stored on the jobsite should not sit in puddles or mud for long. Because structural lumber is kiln dried, any moisture absorbed by lumber will evaporate as long as it is in a well-ventilated area and not exposed to additional sources of moisture.
Testing has shown that moisture content above 19% for approximately one week is required for significant surface mold growth to occur on lumber and/or wood structural building components. Lumber surface mold growth occurs on most species of wood when the moisture content by weight is between 20% and 28%. In most cases, surface mold growth is a superficial phenomenon that does not affect the strength or long-term durability of the wood.
If surface mold growth occurs, it can be removed through relatively straightforward remediation procedures. Surface mold can be scrubbed away with water and detergent, followed by thorough rinsing. The goal of remediation is to remove most of the mold that has grown. It will not kill the mold. Detergents can range from simple dish soap to white vinegar and alkaline mineral salts. Bleach should not be used because the chlorine in bleach does not penetrate the wood fiber, only the water will be absorbed, exacerbating the problem.
Maintaining a lumber moisture content under 19% will prohibit future mold growth. Mold remediation is considered complete when the cleaned area is free of dust and no spore material transfers to a clean cloth when the affected area is wiped down. This approach is the same regardless of the species of mold present.
For further guidance on mold mitigation and remediation, SBCA has published two research reports on these topics:
SRR 1807-01, Mold on Wood Structural Building Components; and